Light emitting device and fluorescent material

ABSTRACT

The present invention is to provide a light emitting device which can generate high-intensity light emission, using a fluorescent material containing a rare earth element ion complex and being excellent in durability and also provide the fluorescent material to be used therein. The present invention relates to a light emitting device comprising a semiconductor light emitting element which emits light within the region from near-ultraviolet light to visible light, and a fluorescent material which contains a rare earth element ion complex having an aromatic ring-containing Bronsted acid ion with a pKa value of 7 or less as a ligand and emits light by the action of light of the semiconductor light emitting element.

TECHNICAL FIELD

The present invention relates to a light emitting device and afluorescent material, and more particularly to a light emitting devicein which a semiconductor light emitting element is combined with afluorescent material, and the fluorescent material used therein.

BACKGROUND ART

Light emitting devices in which light of a discharge lamp or asemiconductor light emitting element is color converted with afluorescent material have hitherto been used for illumination and thelike. In order to generate lights of various colors such as white, in awide color reproduction range, uniformly with a good color renderingproperty by mixing blue, red and green color lights, many studies havebeen made for these light emitting devices. Above all, light emittingdevices using a semiconductor light emitting element such as a lightemitting diode (LED) or a semiconductor laser (LD) have high luminousefficiency and also have an advantage in terms of environmentalprotection such as no use of mercury. Accordingly, the development oflight emitting devices in which an LED or an LD is combined with afluorescent material has been actively carried out.

In particular, light emitting devices in which an LED or an LD iscombined with an organic red fluorescent material comprising a europium(Eu) complex having an anion of a β-diketone as a ligand have beenreported as devices which efficiently absorb light from near-ultravioletlight to visible light and provide high-luminance light emission,compared to a fluorescent lamp using an inorganic red fluorescentmaterial such as Y₂O₃:Eu (see patent document 1 and patent document 2).

Patent Document 1: JP 10-12925 A

Patent Document 2: JP 2000-509912 A

DISCLOSURE OF THE INVENTION

However, the organic red fluorescent material comprising a europium (Eu)complex having an anion of a β-diketone as a ligand, as reported inpatent document 1 and patent document 2, shows a performance of easilysuffering from photo-degradation, and its light emitting ability rapidlydecreases to cause the difficulty of using for a long period of time.Accordingly, the necessity of improving durability has arisen.

The causes of easy photo-degradation on the organic red fluorescentmaterial comprising a europium (Eu) complex having an anion of aβ-diketone as a ligand have been examined. As a result, it has becomeclear that easy dissociation of the β-diketone ligand is one factor. Thepresent inventors have made extensive studies of ligands difficult to bedissociated, and have discovered that a Bronsted acid (anion) derivedfrom an aromatic ring-containing Bronsted acid represented by generalformula (1) shown below, which is a stronger acid than the β-diketone,forms a more stable complex with a rare earth element ion such as aeuropium ion than the β-diketone anion to result in difficulty ofphoto-degradation, and that it emits light by the action of light of asemiconductor light emitting element, thereby arriving at the presentinvention:

wherein R₁ is a group containing at least one aromatic hydrocarbon ringor aromatic heterocycle, each optionally having a substituent group, Xis a divalent connecting group, Q represents a carbon, sulfur orphosphorous atom, a represents 1 or 2, n represents 0 or 1, and prepresents 0 or 1.

The β-diketone anion is an ion formed by dissociation of a hydrogen ion(proton) from the β-diketone, and the β-diketone also corresponds to akind of Bronsted acid. However, the pKa value, a measure of acidstrength, of acetylacetone which is a typical β-diketone is reported tobe 9.3 (Iwanami Koza, Gendai Kagaku (Modern Chemistry) 9, edited byMichinori Oki and Motoharu Tanaka, “Acid-Base and Oxidation-Reduction”,page 34, published by Iwanami Shoten (1979)), and that ofdibenzoylmethane is reported to be 8.59 (Kagaku Binran (Handbook ofChemistry) Kiso-hen II, 5th revision, edited by The Chemical Society ofJapan, page 342, published by Maruzen Co., Ltd. (2004)), and both areweak acids. In order to stabilize the complex, it can be considered thata stronger ionic bond between a rare earth element ion and a ligand ionis desirable. Considering that a stronger acid is desirable, extensivestudies have been made. As a result, it has been found that amongBronsted acids with a pKa value of 7 or less which are stronger acidsthan the β-diketone, an aromatic ring-containing Bronsted acidrepresented by the above-mentioned general formula (1) is resistant tophoto-degradation and solves the problem.

The acid strength of the Bronsted acid which dissociates a proton isindicated by pK_(a), the reciprocal of the logarithm of the equilibriumconstant at the time when it dissociates the proton in an aqueoussolution. The pK_(a) is described in many textbooks, handbooks,encyclopedias and the like such as the above-mentioned “Acid-Base andOxidation-Reduction”, page 27 and “Kagaku Binran Kiso-hen II, 5threvision”, page 331. The pK_(a) values of typical Bronsted acids aredescribed in these books.

The aromatic ring-containing Bronsted acids include many acids slightlysoluble in water. For those acids, the acid strength in the aqueoussolution can be relatively determined by comparing the pK_(a) value in amixed solvent of water and an organic solvent such as ethanol or in anonaqueous solvent such as methanol, ethanol or dimethyl sulfoxide withthe Bronsted acid whose pK_(a) value in the aqueous solution has beenknown.

Accordingly, the present invention has been made in order to solve theproblem which has stood out in relief at the time of developing thelight emitting device using the organic red fluorescent material whichcomprises the Eu complex having such an organic anion as the ligand.That is, objects of the present invention are to provide a lightemitting device which can generate high-intensity light emission, usinga fluorescent material containing a rare earth element ion complex andbeing excellent in durability, particularly a red fluorescent materialcontaining a Eu complex, and also provide a lighting system using thesame, and the fluorescent material used therein.

Thus, the light emitting device to which the present invention isapplied uses a fluorescent material which contains a rare earth elemention complex having an aromatic ring-containing Bronsted acid ion with apKa value of 7 or less as a ligand. That is, the light emitting deviceto which the present invention is applied comprises a semiconductorlight emitting element which emits light within the region fromnear-ultraviolet light to visible light, and a fluorescent materialwhich contains a rare earth element ion complex having an aromaticring-containing Bronsted acid ion with a pKa value of 7 or less as aligand and emits light by the action of light of this semiconductorlight emitting element.

In the light emitting device to which the present invention is applied,the semiconductor light emitting element is preferably a laser diode orlight emitting diode having a peak wavelength within the range of 360 nmto 470 nm. Further, when the ligand in the rare earth element ioncomplex contained in the fluorescent material is one in which thetriplet energy of a mother compound of the Bronsted acid ion is higherthan the excited-state energy level of the rare earth element ion, alight emitting device in which the fluorescent material efficientlyemits light by the action of light of the semiconductor light emittingelement is obtained. Also, it is preferred that the fluorescent materialcontains a rare earth element ion complex having as the ligand aBronsted acid ion represented by the following general formula (2):

wherein R₁ is a group containing at least one aromatic hydrocarbon ringor aromatic heterocycle, each optionally having a substituent group, Xis a divalent connecting group, Q represents a carbon, sulfur orphosphorous atom, a represents 1 or 2, n represents 0 or 1, and prepresents 0 or 1.

Of such fluorescent materials, it is preferred that a rare earth elemention complex having an aromatic ketone group-containing Bronsted acid ionas a ligand is contained. Further, it is usually preferred in terms ofluminance improvement that the fluorescent material contains a rareearth element ion complex having a Lewis base as an auxiliary ligand.This fluorescent material is preferably a resin composition in which therare earth element ion complex is mixed or dispersed.

Furthermore, the light emitting device to which the present invention isapplied further comprises another fluorescent material which emits lightby the action of light of the semiconductor light emitting element,together with the fluorescent material containing the rare earth elemention complex. For example, when the rare earth element ion complex of thepresent invention develops a red color, further inclusion of a bluefluorescent material and a green fluorescent material, each of whichemit light by the action of light of the semiconductor light emittingelement, makes it possible to emit white light having reproducibility ofa color close to natural light. Thereby, it becomes possible to providea lighting system equipped with the light emitting device to which thepresent invention is applied.

Further, referring to the cases where the semiconductor light emittingelement is a blue light emitting element, for example, when the rareearth element ion complex of the present invention emits a red color, itbecomes possible by combination with a green fluorescent material toemit white light excellent in color rendering properties, compared topseudo-white light of only a yellow fluorescent material.

On the other hand, the present invention can be grasped as a fluorescentmaterial containing a rare earth element ion complex having a Bronstedacid ion represented by the following general formula (2) as a ligand:

wherein R₁ is a group containing at least one aromatic hydrocarbon ringor aromatic heterocycle, each optionally having a substituent group, Xis a divalent connecting group, Q represents a carbon, sulfur orphosphorous atom, a represents 1 or 2, n represents 0 or 1, and prepresents 0 or 1.

Further, the rare earth element ion complex preferably has a Lewis baseas an auxiliary ligand.

Furthermore, the above-mentioned Bronsted acid ion is preferably acarboxylic acid or a sulfonic acid, and the above-mentioned rare earthelement ion complex is preferably a europium complex or a terbiumcomplex.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view for illustrating a light emitting device in thisembodiment.

FIG. 2 is a view for illustrating a light emitting mechanism of a Eucomplex for a red fluorescent material.

As for reference numerals in the figures, 10 indicates a light emittingdevice, 11 indicates a semiconductor light emitting element, 12indicates a fluorescent material layer, 13 indicates a mount lead, 14indicates an inner lead, 15 indicates a conductive wire, 16 indicates aconductive wire, 17 indicates a sealing resin portion, 18 indicates abracket, and 19 indicates an electric contact.

BEST MODE FOR CARRYING OUT THE INVENTION

The light emitting device to which this embodiment is applied isillustrated below, but the following illustration is one example(typical example) of embodiments, and the device is not specified bythese contents.

FIG. 1 is a view for illustrating the light emitting device in thisembodiment. The light emitting device 10 shown in FIG. 1 comprises abracket 18, a mount lead 13 and an inner lead 14 which are attached tothe bracket 18, an electric contact 19 which is attached to a lowerportion of the bracket 18 and conductive to the mount lead 13 and theinner lead 14, a semiconductor light emitting element 11 housed in a cupof an upper portion of the mount lead 13, a fluorescent material layer12 in which a red fluorescent material is mixed and dispersed in abinder resin, and which is provided so as to cover the semiconductorlight emitting element 11, a conductive wire 15 which makes the innerlead 14 and the semiconductor light emitting element 11 conductive toeach other, a conductive wire 16 which makes the semiconductor lightemitting element 11 and the mount lead 13 conductive to each other, anda sealing resin portion 17 which is formed on an upper portion of thebracket 18 in a dome form and seals these semiconductor light emittingelement 11, fluorescent material layer 12, mount lead 13, inner lead 14,conductive wire 15 and conductive wire 16.

The semiconductor light emitting element 11 emits light within theregion from near-ultraviolet light to visible light, and a fluorescentmaterial contained in the fluorescent material layer 12 absorbs thislight to emit visible light having a longer wavelength. As thesemiconductor light emitting element 11, there is used a laser diode(LD) or light emitting diode (LED) having a peak wavelength ranging from360 nm to 470 nm in a light emission spectrum. Although such a laserdiode (LD) or light emitting diode (LED) is not particularly limited,for example, an LD or LED having a peak wavelength of 380 nm to 470 nm,more preferably a peak wavelength in a longer visible light region than400 nm is preferred. In the semiconductor light emitting element inwhich the peak wavelength is excessively on the short wavelength side,organic compounds such as a complex and a resin are liable todeteriorate by light. This is therefore unfavorable. On the other hand,when the peak wavelength is excessively on the long wavelength side, thetriplet energy level of a ligand of a rare earth element ion complexdecreases to narrow the range of choice for a light-emittable ligand.This is therefore unfavorable.

The fluorecent material contained in the flurorescent material layer 12contains a rare earth element ion complex having an aromaticring-containing Bronsted acid ion with a pKa value of 7 or less as aligand. Above all, a Bronsted acid ion represented by general formula(2) shown below, which is derived from an aromatic ring-containingBronsted acid represented by general formula (1) shown below, ispreferably used as the ligand:

wherein R₁ is a group containing at least one aromatic hydrocarbon ringor aromatic heterocycle, each optionally having a substituent group, Xis a divalent connecting group, Q represents a carbon, sulfur orphosphorous atom, a represents 1 or 2, n represents 0 or 1, and prepresents 0 or 1.

The Bronsted acid represented by general formula (1) is converted to theBronsted acid ion represented by general formula (2) by dissociation ofa proton (H⁺) from an OH group.

Typical examples of the aromatic ring-containing Bronsted acid with apK_(a) value of 7 or less are a carboxylic acid, a sulfonic acid, asulfinic acid and a phosphinic acid. In general formula (1), when Q is acarbon atom, a=1 and p=0, thus resulting in a carboxylic acid. When Q isa sulfur atom, a=1, resulting in a sulfinic acid in the case of p=0, anda sulfonic acid in the case of p=1. When Q is a phosphorus atom, a=2 andp=0, resulting in a phosphonic acid.

Of these, the carboxylic acid and the sulfonic acid are preferred interms of the degree of freedom of synthesis and stability. Thecarboxylic acid has a feature that a complex having high luminescenceintensity is easily obtained, and the sulfonic acid has a feature that acomplex in which the excitation wavelength is made longer is easilyobtained.

Further, the ligand represented by general formula (2) contains at leastone aromatic ring, and has 8 or more π electrons. It is preferred interms of an absorption wavelength region that a Bronsted acid ionconstituting a π-conjugated system is used as the ligand. Furthermore,the number of the aromatic rings is not particularly limited, as long asthe triplet energy of a mother compound of the Bronsted acid ion ishigher than the excited-state energy level of the rare earth elemention. In the case of a europium ion complex or a terbium ion complex, itis usually preferred to use a tricyclic or less cyclic aromatic ring oraromatic heterocycle as the aromatic ring. When the number of condensedaromatic rings is 4 or more, for example, in a compound having fouraromatic rings such as pyrene, the triplet energy excited by absorbinglight from the semiconductor light emitting element 11 decreases, sothat there is the possibility that the rare earth element ion complexbecomes impossible to emit light.

R₁ in general formula (2) is preferably a monovalent group derived froma tricyclic or less cyclic aromatic hydrocarbon ring or aromaticheterocyclic ring, each optionally having a substituent group. Thearomatic hydrocarbon rings include, for example, aromatic monocyclichydrocarbons or aromatic condensed polycyclic hydrocarbons such asbenzene, naphthalene, indene, biphenyl, acenaphthene, fluorene,phenanthrene, tetralin, indan and indene; compounds derived fromaromatic hydrocarbons such as benzoquinone, naphthoquinone andanthraquinone; and the like. The aromatic heterocyclic rings includearomatic monocyclic heterocycles or aromatic condensed polycyclicheterocycles such as furan, pyrrole, thiophene, oxazole, isoxazole,thiazole, imidazole, pyridine, benzofuran, benzothiophene, coumarin,benzopyran, carbazole, xanthene, quinoline, triazine, dibenzofuran,dibenzothiophene, chroman, pyrazoline, pyrazolone and flavone; and thelike

Further, the substituent groups which R₁ optionally has include an alkylgroup such as methyl, ethyl, propyl or butyl; a fluoroalkyl group suchas trifluoromethyl or pentafluoroethyl; a cycloalkyl group such as acyclohexyl group; an ethynyl group; an arylethynyl group such asphenylethynyl, pyridylethynyl or thienylethynyl; an alkoxy group such asmethoxy or ethoxy; an aryl group such as phenyl or naphthyl; an aralkylgroup such as benzyl or phenethyl; an aryloxy group such as phenoxy,naphthoxy or biphenyloxy; a hydroxyl group; an allyl group; an acylgroup such as acetyl, propionyl, benzoyl, toluoyl or biphenylcarbonyl;an acyloxy group such as acetoxy, propionyloxy or benzoyloxy; analkoxycarbonyl group such as methoxycarbonyl or ethoxycarbonyl; anaryloxycarbonyl group such as phenoxycarbonyl; a carboxyl group; acarbamoyl group; an amino group; a substituted amino group such asdimethylamino, diethylamino, methylbenzylamino, diphenylamino oracetylmethylamino; a substituted thio group such as methylthio,ethylthio, phenylthio or benzylthio; a mercapto group; a substitutedsulfonyl group such as ethylsulfonyl or phenylsulfonyl; a cyano group; ahalogen group such as fluoro, chloro, bromo or iodo; and the like.

Of these, preferred are an alkyl group having 1 to 4 carbon atoms, analkoxy group, an aryl group, a cycloalkyl group, an aryloxy group, anaralkyl group, an ethynyl group and a halogen group. R₁ is not limitedto these substituent groups. These substituent groups may further have asubstituent group.

Then, the Bronsted acid ion represented by general formula (2) isdivided into the case where it does not have X as a divalent connectinggroup (n=0) and the case where it has X (n=1). Further, when it has X asa divalent connecting group (n=1), X is divided into two types of forms,the case where it has a carbonyl group and the case where it has nocarbonyl group. Accordingly, the Bronsted acid ion represented bygeneral formula (2) is further represented by general formula (3) shownbelow having no carbonyl group and general formula (4) shown belowhaving a carbonyl group. As the rare earth element ion complex, therecan be used any of complex structures in which these Bronsted acid ionsare used as the ligands.

In general formula (3) and general formula (4), R₂ may be any, as longas it acts as a divalent connecting group. Examples thereof include analkylene group, a divalent connecting group derived from aring-assembled hydrocarbon and a divalent connecting group derived froman aliphatic ring, an aromatic ring or a heterocycle, and the like. Ingeneral formula (4), m is 0 or 1.

The alkylene groups of R₂ include methylene, ethylene and-the like. Thering-assembled hydrocarbons include biphenyl, terphenyl, binaphthyl,cyclohexylbenzene, phenylnaphthalene and the like. The aliphatic ringsinclude cyclopentane, cyclohexane, cycloheptane, norbornane,bicyclohexyl and the like. The aromatic rings include the same compoundsas the specific examples of the aromatic rings described above. Theheterocycles include, as well as the aromatic heterocycles describedabove, aliphatic heterocycles such as pyrazoline, piperazine,imidazolidine and morpholine. In addition, R₂ includes thioalkylenessuch as —SCH₂; oxyalkylenes such as —OCH₂— and —OCH₂CH₂—; vinylene(—C═C—); and the like. R₂ is not limited to these divalent substituentgroups, but a conjugated system-forming group such as an aromatic ringis preferred, and a phenylene group and a naphthylene group isparticularly preferred. These divalent substituent groups may furtherhave a substituent group.

Of the Bronsted acids represented by general formula (1), when Q is acarbon atom and p is 1, that is, specific examples of the carboxylicacids from which the carboxylic acid ion is derived are exemplifiedbelow. The carboxylic acid used in this embodiment is not limitedthereto. In general formula (1), when n is 0, compounds include thefollowing carboxylic acids (1 to 10):

Next, in general formula (1), when n is 1 and X is R₂ (general formula(3)), compounds include the following carboxylic acids (11 to 15 and A-1to A-3):

Then, in general formula (4), when m is 0, compounds include thefollowing carboxylic acids (16, 17 and B-1 to B-5):

In general formula (4), when m is 1, R₁ is a phenyl group and R₂ is aphenylene group, compounds include the following carboxylic acids (18 to30, C-1 and C-2):

In general formula (4), when m is 1, R₁ is a phenyl group and R₂ is anaphthylene group, compounds include the following carboxylic acids (31to 34):

In general formula (4), when m is 1, R₁ is a phenyl group and R₂ isanother group, compounds include the following carboxylic acids (35 to37 and D-1 to D-3):

In general formula (4), when m is 1, R₁ is a naphthyl group and R₂ is anaromatic hydrocarbon ring, compounds include the following carboxylicacids (38 to 41, E-1 and E-2):

In general formula (4), when m is 1, R₁ is a naphthyl group and R₂ isanother group, compounds include the following carboxylic acids (42 to44 and F-1):

In general formula (4), when m is 1, R₁ is an acenaphthyl group and R₂is a phenylene group or another group, compounds include the followingcarboxylic acids 45 to 48 and G-1):

In general formula (4), when m is 1, R₁ is a fluorenyl group and R₂ is aphenylene group, compounds include the following carboxylic acids (50 to55 and H-1 to H-9):

In general formula (4), when m is 1, R₁ is a phenanthrenyl group and R₂is a phenylene group or another group, compounds include the followingcarboxylic acids (56 to 59):

In general formula (4), when m is 1, R₁ is a heterocyclic group and R₂is a phenylene group, compounds include the following carboxylic acids(60, 61 and I-1 to I-21):

In general formula (4), when m is 1, R₁ is another group and R₂ is aphenylene group, compounds include the following carboxylic acids (J-1to J-4):

The carboxylic acid from which the carboxylic acid ion is derived can besynthesized by known methods. Synthesis methods are described, forexample, in Shin-Jikken Kagaku Koza (New Course for ExperimentalChemistry), Vol. 14, “Synthesis and Reaction of Organic Compounds (II)”,page 921, edited by The Chemical Society of Japan (1977), Jikken KagakuKoza (Course for Experimental Chemistry), 4th Ed., Vol. 22, “OrganicSynthesis”, page 1, edited by The Chemical Society of Japan (1992) orthe like. Typical examples of the synthesis methods include an oxidationreaction of a corresponding primary alcohol or aldehyde, a hydrolysisreaction of an ester or a nitrile, a Friedel-Craft reaction by an acidanhydride, and the like.

In particular, according to the Friedel-Craft reaction using phthalicanhydride, naphthalic anhydride, succinic anhydride, diphenic anhydride,1,2-cyclohexanedicarboxylic acid anhydride, 2,3-pyridazinecarboxylicacid anhydride or the like, a carboxylic acid having a carbonyl group inits molecule can be synthesized. For example, according to theFriedel-Craft reaction using an aromatic hydrocarbon or an aromaticheterocycle and phthalic anhydride, a carboxylic acid in which acarbonyl group is bonded to the ortho-position of a benzene ring can beeasily synthesized, as shown in the reaction formula below. Thecarboxylic acid in which a carbonyl group is bonded to theortho-position of a benzene ring is preferred, because a complex havinghigh luminance is easily obtained compared to the para-substituted one.

Of the Bronsted acids represented by general formula (1), when Q is asulfur atom and p=1, that is, specific examples of the sulfonic acidsfrom which the sulfonic acid ion is derived are exemplified below. Thesulfonic acid used in this embodiment is not limited thereto. In generalformula (1), when n is 0, compounds include the following sulfonic acids(K-1 to K-6):

Next, in general formula (1), when n is 1 and X is R₂ (general formula(3)), compounds include the following sulfonic acids (L-1 to L-3):

Then, in general formula (4), when m is 1, R₁ is a phenyl group and R₂is an aromatic hydrocarbon ring, compounds include the followingsulfonic acid (M-1):

Then, in general formula (4), when m is 1, R₁ is a fluorenyl group andR₂ is a phenylene group or another group, compounds include thefollowing sulfonic acids (N-1 and N-2):

In general formula (4), when m is 1, R₁ is a heterocyclic group and R₂is a phenylene group or another group, compounds include the followingsulfonic acids (O-1 to O-6):

Synthesis methods of the sulfonic acid are described, for example, inShin-Jikken Kagaku Koza (New Course for Experimental Chemistry), Vol.14, “Synthesis and Reaction of Organic Compounds [III]”, page 1773,edited by The Chemical Society of Japan, published by Maruzen Co., Ltd.(1978), and the like. Typical examples of the synthesis methods of thearomatic sulfonic acid include a sulfonation reaction by fuming sulfuricacid, and a hydrolysis method of sulfonyl chloride synthesized bychlorosulfonic acid. In addition, the sulfonic acid can also besynthesized by a Friedel-Craft reaction using 2-sulfobenzoic acidanhydride as shown by the following formula:

Of the Bronsted acids represented by general formula (1), when Q is asulfur atom and p=0, that is, specific examples of the sulfinic acidsfrom which the sulfinic acid ion is derived are exemplified below. Thesulfinic acid used in this embodiment is not limited thereto. In generalformula (1), when n is 0, compounds include the following sulfinic acids(P-1 to P-6):

Next, in general formula (1), when n is 1 and X is R₂ (general formula(3)), compounds include the following sulfinic acids (Q-1 to Q-5):

In general formula (4), when m is 1, R₁ is a phenyl group and R₂ is aphenylene group, compounds include the following sulfinic acids (R-1 andR-2):

Of the Bronsted acids represented by general formula (1), when Q is aphosphorus atom and p=0, that is, specific examples of the phosphinicacids from which the phosphinic acid ion is derived are exemplifiedbelow. The phosphinic acid used in this embodiment is not limitedthereto. In general formula (1), when n is 0, compounds include thefollowing phosphinic acids (S-1 and S-2):

Next, in general formula (1), when n is 1 and X is R₂ (general formula(3)), compounds include the following phosphinic acid (T-1):

In the light emitting device 10 to which this embodiment is applied, thefluorescent material contained in the fluorescent material layer 12containing the rare earth element ion complex having the specificaromatic group-containing Bronsted acid ion as the ligand absorbs lightfrom the semiconductor light emitting element 11 and emits visible lighthaving a longer wavelength, as described above. As the mechanism oflight emission of the rare earth element ion complex, there is known themechanism that the ligand absorbs light from the light emitter andexcitation energy thereof transfers to the rare earth element ioncomplex to excite it, thereby emitting light. When the excitation energylevel of the ligand is too low, energy transfer does not occur,resulting in failure to emit light. For example, in the case ofeuropium, this mechanism is illustrated with reference to FIG. 2.

That is, as shown in FIG. 2, the ligand goes into an excited singlet(S1) state on absorption of light, and intersystem crossing is carriedout therefrom to an excited triplet (T₁) state. Then, energy transfer isperformed from the T₁ state to an excited state of the rare earthelement ion. In this case, the transfer of energy higher than anexcited-state level of a light emission level is required. In the caseof energy lower than the light emission level, light emission does notoccur as a matter of course. The rare earth ion excited by energytransfer emits light by transition from a light emission level high intransition probability to a base state. In a europium ion (Eu³⁺), it hasbeen considered that transition from ⁵D₀ to ⁷F₂ causes light emission ofa red color which is a main component. In a terbium ion (Tb³⁺), lightemission of a green color from a light emission level ⁵D₄ occurs. Lightemission spectra of these trivalent rare earth ions are described in thefollowing literature (Kidorui no Kagaku (Science of Rare Earths),written and edited by Ginya Adachi, page 154, Kagaku Dojin (1999)).Further, the effect of energy of the triplet state in the mechanism ofenergy transfer has been reported in studies in which the triplet energy(T₁) of a ligand molecule and light emission of a Eu complex aremeasured and the relationship therebetween is discussed (for example,Bulletin of The Chemical Society of Japan, Vol. 43, 1955-1962 (1970)etc.)

In the light emitting device 10 to which this embodiment is applied, itis desirable that the T₁ level of the aromatic ring-containing Bronstedacid used as the ligand of the rare earth element ion complex has energyhigher than the excited-state level of the rare earth element ion. As aresult of studies of various Bronsted acids, in the Bronsted acid ion asthe ligand for light emission of the rare earth element ion complex, itis necessary that at least the triplet energy of the mother compound ofthe Bronsted acid ion has a higher value than the excited-state energylevel of the rare earth element ion.

Further, for example, in the case of an ion derived from coumarincarboxylic acid as the ligand of the europium complex, the tripletenergy of coumarin carboxylic acid is 255 kJ/mol, the triplet energy ofcoumarin which is a mother compound thereof is 258 kJ/mol, and thedifference therebetween is 3 kJ/mol. It is therefore preferred that thetriplet energy of the mother compound is 3 kJ/mol or more higher thanthe excited-state energy level of the europium ion.

The ⁵D₁ level of the Eu³⁺ ion is reported to be 19,100 cm⁻¹ (228.5kJ/mol) (Chemical Review, Vol. 82, pages 541-552 (1982)), and it hasbeen confirmed that the Eu complex having the Bronsted acid ion ofanthracene (176 kJ/mol) or pyrene (202 kJ/mol), which has a tripletenergy lower than this, as the ligand does not emit light. The tripletenergy can be measured from a phosphorescence spectrum of a solution.Data books in which triplet energy values of compounds are collected canbe consulted. Tables in which data are collected include, for example,Hikari to Kagaku no Jiten (A Dictionary of Light and Chemistry), editedby Editorial Board of Hikari to Kagaku no Jiten, pages 550-605, MaruzenCo., Ltd. (2002), and the like.

As the rare earth element ion complex contained in the fluorescentmaterial contained in the fluorescent material layer 12, there isgenerally used, from the viewpoint of luminance, a rare earth elemention complex represented by general formula (5), which has two Lewis basecompounds as an auxiliary ligand based on one rare earth element ion:A₃LD_(r)  (5)wherein A represents the Bronsted acid ion of the above-mentionedgeneral formula (2) which may be different from one another, Lrepresents a rare earth element ion, D represents an auxiliary ligandcomprising a Lewis base, and r represents 0, 1 or 2.

Although the Lewis base compound (D) used as the auxiliary ligand is notparticularly limited, it is usually selected from Lewis base compoundshaving a nitrogen atom or oxygen atom which can coordinate to the rareearth element ion. Examples thereof include an amine, an amine oxide, aphosphine oxide and a sulfoxide, each optionally having a substituentgroup, and the like. The two Lewis base compounds used as the auxiliaryligand may be compounds different from each other or the same compound.

For specific examples of the Lewis base compounds (D) used as theauxiliary ligand, for example, the amines include pyridine, pyrazine,quinoline, isoquinoline, phenanthridine, 2,2′-bipyridine,1,10-phenanthroline and the like. The amine oxides include N-oxides ofthe above-mentioned amines such as pyridine-N-oxide and2,2′-bipyridine-N,N′-dioxide. The phosphine oxides includetriphenylphosphine oxide, trimethylphosphine oxide, trioctylphosphineoxide and the like. The sulfoxides include diphenyl sulfoxide, dioctylsulfoxide and the like.

Of these Lewis base compounds, when there exist two coordinated atoms ina molecule, for example, two nitrogen atoms or the like, such asbipyridine and phenanthroline, one Lewis base compound may be allowed toact as two auxiliary ligands. As the substituent groups to besubstituted to these Lewis base compounds, there are exemplified thesubstituent groups described above. Above all, particularly preferredare an alkyl group, an aryl group, an alkoxyl group, an aralkyl group,an aryloxy group, a halogen group and the like.

Specific examples (1 to 23) of the Lewis base compounds (D) used as theauxiliary ligand are exemplified below. However, the Lewis basecompounds used in this embodiment should not be construed as beinglimited thereto.

When the rare earth element ion complex of the present invention isproduced, it sometimes happens that crystallization is difficult, orthat the auxiliary ligand is not incorporated, depending on the kind ofBronsted acid of a raw material. Accordingly, different kinds ofBronsted acids such as those having different substituent groups may beused as a mixture.

The Bronsted acid to be mixed may be a Bronsted acid having no aromaticring, but the aromatic ring-containing Bronsted acid represented by theabove-mentioned general formula (1) is preferred. In this case, themixture may be either a mixture of Bronsted acids of the same kind suchas carboxylic acids or sulfonic acids, or a mixture of different kindsof Bronsted acids such as a combination of a carboxylic acid and asulfonic acid.

The rare earth element ion complex of the present invention can beeasily synthesized by mixing a solution of a rare earth element halideor the like with a solution containing the above-mentioned Bronsted acidwhich acts as the ligand, a Lewis base which acts as the auxiliaryligand and a base.

As a solvent used in the ligand solution, there is used an alcohol suchas methanol, ethanol or isopropanol. There is also available an organicsolvent such as a ketone such as acetone or methyl ethyl ketone, anether such as tetrahydrofuran or dimethoxyethane, dimethyl sulfoxide ordimethylformamide. When the acid is slightly soluble in an alcohol, amixed solvent with these organic solvents is used.

As the base, there is used an amine such as triethylamine,triethanolamine, diethanolamine or piperidine, as well as an alkalihydroxide such as sodium hydroxide or potassium hydroxide. As a solventfor dissolving the salt of the rare earth element, there is used theabove-mentioned alcohol, as well as water.

The complex is usually deposited as a precipitate immediately on mixingof the above-mentioned solution. The complex can be obtained byfiltering and washing the deposited precipitate. When the resultingcomplex is recrystallized, a high-purity complex is obtained, impuritieswhich inhibit light emission can be removed, and a crystalline complexhaving high luminous efficiency can be obtained. The precipitatedeposited by the reaction is amorphous in some cases, and containsimpurities in many cases. In order to increase luminous efficiency, apurification process is important. When the complex of the presentinvention is used as it is in a solid state, the luminous efficiencychanges depending on the crystal form or the growth state of a crystalin many cases. Accordingly, treatment for obtaining the optimum crystalform or crystal growth state is also important. As the treatmentmethods, there can be used crystal form conversion treatment methodswhich are usually performed in organic pigments or crystals, such asheat treatment in an organic solvent, mechanical irritation and heattreatment, as well as the above-mentioned recrystallization.

The rare earth element complexes of the present invention formfluorescent materials of various luminescent colors by the rare earthelement ions. The europium (Eu) complex forms a red fluorescentmaterial, and the terbium (Tb) complex forms a green fluorescentmaterial. In addition, a blue fluorescent material is obtained by athulium (Tm) complex, yellow to orange fluorescent materials areobtained by respective fluorescent materials of holmium (Ho), erbium(Er), samarium (Sm) and dysprosium (Dy), and a red fluorescent materialis obtained by a praseodymium (Pr) fluorescent material. The Bronstedacid ion which forms the ligand of each of these complexes is selectedfrom acids having triplet energy higher than the excited-state energylevel relating to light emission of the rare earth element ion.

The compounds specified in the present invention are usually solid intheir state, and emit light by the action of light from thesemiconductor light emitting element. The molecular weight thereof isusually from about 800 to 3,500.

In the light emitting device 10 to which this embodiment is applied, thefluorescent material layer 12 is prepared, for example, as a mixed resincomposition obtained by dissolving or dispersing the europiumcomplex-containing red fluorescent material in an appropriate binderresin, and arranged by coating or other methods at a position wherelight from the semiconductor light emitting element 11 is absorbed.Further, in the case of a cannonball form which is the general form ofLEDs, the red fluorescent material can also be mixed in the sealingresin such as an epoxy resin. In this case, light from the redfluorescent material becomes light more diffused.

The resins used for preparing the mixed resin composition obtained bydissolving or dispersing the rare earth element ion complex-containingfluorescent material in the appropriate binder resin usually include athermoplastic resin, a thermosetting resin, a photo-curing resin and thelike. Specific examples thereof include a methacrylic resin such aspolymethyl methacrylate; a styrenic resin such as polystyrene or astyrene-acrylonitrile copolymer; a polycarbonate resin; a polyesterresin; a phenoxy resin; a butyral resin; polyvinyl alcohol; a cellulosicresin such as ethyl cellulose, cellulose acetate or cellulose acetatebutyrate; an epoxy resin; a phenol resin; a silicone resin; and thelike.

The light emitting device 10 to which this embodiment is applied furtherhas another fluorescent material, for example, a fluorescent materialcontaining rare earth element ion complexes different from each other,an inorganic fluorescent material or the like, in addition to the rareearth element ion complex exemplified in this embodiment. Specifically,it further has a blue fluorescent material and a green fluorescentmaterial, together with the europium complex-containing red fluorescentmaterial, and a combination of these makes it possible to emit whitelight. As the blue fluorescent material or the green fluorescentmaterial, there can be used a known fluorescent material.

For example, the blue fluorescent materials include an organicfluorescent material comprising a fluorescent dye such as a naphthalicacid imide-based, a benzoxazole-based, a styryl-based, a coumarin-based,a pyrazoline-based or a triazole-based one, or an inorganic fluorescentmaterial such as ZnS:Ag, Sr₅(PO₄)₃Cl:Eu or BaMgAl₁₀O₁₇:Eu. Further, thegreen fluorescent materials include an organic fluorescent materialcomprising a benzoxazinone-based, a quinazolinone-based, acoumarin-based, a quinophthalone-based or a naphthalic acid imide-basedone, or an inorganic fluorescent material such as ZnS:Cu, ZnS:CuAl,BaMgAl₁₀O₁₇:Eu or Mn. In addition, the blue fluorescent materialsinclude an organic fluorescent material such as a thulium complex, andthe green fluorescent materials include an organic fluorescent materialsuch as a terbium complex. As the ligands of these complexes, there canbe used aromatic group-containing Bronsted acid ions used as the ligandsof complexes in this embodiment, as well as the known ligands.

White light is emitted by arranging a fluorescent material resin layercontaining a mixture of a red fluorescent material, a blue fluorescentmaterial and a green fluorescent material on the semiconductor lightemitting element 11. In this case, the red fluorescent material, theblue fluorescent material and the green fluorescent material are notnecessarily mixed in the same resin, and a resin layer containing thered fluorescent material may be laminated on a resin layer containingthe blue fluorescent material and the green fluorescent material.

Further, when the semiconductor light emitting element is a blue lightemitting element, for example, a fluorescent material resin layercontaining a mixture of the rare earth element ion complex of thepresent invention which emits red light and a green fluorescent materialis arranged on the semiconductor light emitting element 11.

The light emitting devices 10 to which this embodiment is applied can beused alone or as a combination of the plurality of them, for example, asvarious lighting systems such as a lighting lamp, a back light for aliquid crystal panel or the like and ultrathin type illumination, anddisplay units. Further, the rare earth element ion complex having thespecific aromatic ring-containing Bronsted acid ion as the ligand, whichis used in the light emitting device 10 to which this embodiment isapplied, particularly, the europium complex having the carboxylic acidion as the ligand has high light stability, compared to a conventionaleuropium complex having a β-ketone as the ligand. As a result, the lightemitting device 10 having durability is obtained.

EXAMPLES

This embodiment will be illustrated in greater detail with reference tothe following examples, but this embodiment should not be construed asbeing limited thereto. Further, all the parts and percentages in theexamples are given by weight unless otherwise specified.

(Light Stability Test of Red Fluorescent Material)

One part of a powder of a europium (Eu) complex and 200 parts of adichloromethane solution (concentration: 20%) of polyvinyl butyral weremixed. The resulting mixed solution was applied onto a glass slide witha bar coater, and dried to prepare a resin layer having a film thicknessof 20 μm. For this resin layer, a light stability test was performedusing a light stability tester (Atlas Ci4000, manufactured by Toyo SeikiSeisaku-Sho Ltd.) under conditions of 58° C., a humidity of 50% andlight emission for 2 hours to measure the residual ratio of a redfluorescent material. The larger numerical value indicates the betterweather resistance (unit: %).

(Triplet Energy Values of Mother Compounds of Carboxylic Acid Ions)

The triplet energy values of the mother compounds (R₁—(X)_(n)—H) (1 to12) of the mother compounds of the carboxylic acid ions represented bygeneral formula (1) were obtained from the above-mentioned literature(Hikari to Kagaku no Jiten (A Dictionary of Light and Chemistry), editedby Editorial Board of Hikari to Kagaku no Jiten, pages 550-605, MaruzenCo., Ltd. (2002)), and are shown in Table 1.

TABLE 1 Triplet Energy Eu Complex R₁—(X)n—H (kJ mof⁻¹) R₁—(X)n—COOHEmission 1

331

Observed 2

287

Observed 3

287

Observed 4

287

Observed 5

282

Observed 6

261

Observed 7

260

Observed 8

258

Observed 9

258

Observed 10 

211

Notobserved 11 

203

Notobserved 12 

178

Notobserved

Example 1

Using as raw materials carboxylic acids of 1 to 9 shown in Table 1 andphenanthroline as an auxiliary ligand, europium complexes weresynthesized. For the nine kinds of europium complexes synthesized, thepresence or absence of red light emission was measured by an LEDemitting ultraviolet light of 375 nm. The results thereof are shown inTable 1.

From the results of Table 1, the triplet energies of the carboxylicacids of 1 to 9 were higher than the excited-state energy level of theeuropium ion (about 229 kJ/mol). For all the europium complexes usingthese carboxylic acids, good red light emission was observed by the LEDemitting ultraviolet light of 375 nm. Further, with respect to thetriplet energies of a mother compound and the carboxylic acid, in thecase of coumarin, the triplet energy of coumarin is 258 kJ/mol, and thatof coumarin carboxylic acid derived from coumarin is 255 kJ/mol. Thedifference therebetween is as small as 3 kJ/mol, so that it is shownthat the triplet energy value of the mother compound gives anindication.

Comparative Example 1

Using as raw materials carboxylic acids of 10 to 12 shown in Table 1 andphenanthroline as an auxiliary ligand, europium complexes weresynthesized in the same manner as in Example 1. For the three kinds ofeuropium complexes synthesized, the presence or absence of red lightemission was measured by an LED emitting ultraviolet light of 375 nm.The results thereof are shown in Table 1. From the results of Table 1,the triplet energies of the carboxylic acids of 10 to 12 were lower thanthe excited-state energy level of the europium ion (about 229 kJ/mol).All the europium complexes using these carboxylic acids did not emitlight by the LED emitting ultraviolet light of 375 nm.

Example 2

Evaluation of light stability was performed using a europium (Eu)complex having a structure shown below. As a result, the residual ratioof a red fluorescent material showed 96%, and the light stability wasgood.

Example 3

Evaluation of light stability was performed in the same manner as inExample 2 with the exception that a Eu complex having a structure shownbelow was used in place of the Eu complex used in Example 2. As aresult, the residual ratio of a red fluorescent material showed 90%, andthe light stability was good.

Comparative Example 2

Evaluation of light stability was performed in the same manner as inExample 2 with the exception that Eu(TTA)₃Phen (wherein TTA represents1-(2-thenoyl)-4,4,4-trifluoro-1,3-butanedionate, and Phen represents1,10-phenanthroline), a β-diketone-based complex having a structureshown below, was used in place of the Eu complex used in Example 2. As aresult, the residual ratio of a red fluorescent material showed about10%, resulting in poor light stability.

Comparative Example 3

Evaluation of light stability was performed in the same manner as inExample 2 with the exception that Eu(DBM)₃Phen (wherein DBM representsdibenzoylmethane), a β-diketone-based complex having a structure shownbelow, was used in place of the Eu complex used in Example 2. As aresult, the residual ratio of a red fluorescent material showed about18%. From these results, it is known that the carboxylic acid-basedcomplexes are substantially excellent in light stability, compared tothe diketone-based complexes.

Example 4

A powder of the Eu complex used in Example 2 was packed into a metalcell having a diameter of 10 mm and a depth of 2 mm, and the lightemission spectral intensity thereof was measured. For comparison, apowder of an inorganic red fluorescent material Y₂O₂S:Eu was similarlymeasured. The light emission intensities of peak wavelengths of lightemission spectra at light excitation of 375 nm were compared. As aresult, in the Eu complex used in Example 2, a light emission spectralintensity of about 1.6 times that of the powder of the inorganic redfluorescent material Y₂O₂S:Eu was observed.

Example 5

The light emission intensities of peak wavelengths of light emissionspectra at light excitation of 395 nm were compared in the same manneras in Example 4 with the exception that the Eu complex was replaced bythe Eu complex used in Example 3. As a result, in the Eu complex used inExample 3, a light emission spectral intensity of about 1.5 times thatof the powder of the inorganic red fluorescent material Y₂O₂S:Eu wasobserved.

Example 6

The Eu complex used in Example 2, a blue fluorescent material (Sr, Ca,Ba, Mg)₁₀(PO₄)₆Cl:Eu and a green fluorescent material ZnS:Cu, Au, Alwere mixed at a ratio of 22:15:63 by weight, and the resulting mixturewas dispersed in an aqueous solution of polyvinyl alcohol. The resultingdispersion was applied onto a glass slide and dried to prepare afluorescent material layer. This fluorescent material layer wasirradiated with ultraviolet light of an LED (product name: NSHU 550,manufactured by Nichia Corporation) having a peak wavelength of 375 nmto obtain white light having neutral white 5000 K chromaticitycoordinates (x, y=(0.345, 0.354).

Example 7 Synthesis of Eu(AQ2CA)₃Phen

In 100 ml of a mixed solvent of ethanol/water=100/3 (volume ratio), 0.76g (3.0 mmol) of anthraquinone-2-carboxylic acid (hereinafter referred toas AQ2CA), 0.20 g (1.0 mmol) of 1,10-phenanthroline monohydrate and 0.32g (3.0 mmol) of 2,2′-iminodiethanol were dissolved under reflux. To thissolution, a solution obtained by dissolving 0.37 g (1 mmol) of europiumchloride (III) hexahydrate in 20 ml of ethanol was added dropwise underreflux taking 2 hours, followed by further reflux for 1 hour. Then,after retention at 60° C. for 1 hour and further at 40° C. for 1 hour,the resulting solution was allowed to cool to room temperature. Aprecipitate thus formed was filtered by suction, and washed withethanol. The resulting light yellow powder was dried under vacuum at 80°C., and then, heat treated at 160° C. for 1 hour to obtainEu(AQ2CA)₃Phen.

The light emission spectrum at excitation of 405 nm of thisEu(AQ2CA)₃Phen was confirmed. As a result, there was obtained a lightemission intensity of 2.3 times in the area ratio of the light emissionspectrum, and that of 2.0 times in the light emission intensity ratio atthe peak wavelength of the light emission spectrum, compared to aninorganic fluorescent material La₂O₂S:Eu (KX-681 manufactured by KaseiOptonix, Ltd.). The “area of the light emission spectrum” as used in thepresent invention means the integrated intensity of the light emissionspectrum observed in the wavelength range of 500 nm to 600 nm. Further,a light emission excitation spectrum was measured. As a result, lightwas emitted at approximately equal intensity even by light having alonger wavelength than 420 nm, and the excitation wavelength wassubstantially shifted to the long wavelength side, compared to theinorganic fluorescent material La₂O₂S:Eu.

Example 8 Synthesis of Eu(p-DBFBA)₃Phen

In 60 ml of a mixed solvent of tetrahydro-furan/acetonitrile=2/3 (volumeratio), 0.32 g (1.0 mmol) of p-DBFBA represented by the structure shownbelow, 0.07 g (0.33 mmol) of 1,10-phenanthroline monohydrate and 0.11 g(1.0 mmol) of 2,2′-iminodiethanol were dissolved under reflux. To thissolution, a solution obtained by dissolving 0.12 g (0.33 mmol) ofeuropium chloride (III) hexahydrate in 20 ml of a mixed solvent ofethanol/acetonitrile=1/3 (volume ratio) was added dropwise under refluxtaking 1 hour. Then, after retention at 60° C. for 1 hour and further at50° C. for 1 hour, the resulting solution was allowed to stand at roomtemperature for about 15 hours. A precipitate thus formed was filteredby suction, and washed with ethanol. The resulting white powder wasdried under vacuum at 80° C., and then, heat treated at 160° C. for 1hour to obtain Eu(p-DBFBA)₃Phen.

The light emission spectrum at excitation of 405 nm of thisEu(p-DBFBA)₃Phen was confirmed. As a result, there was obtained a lightemission intensity of 2.2 times in the area ratio of the light emissionspectrum, and that of 2.0 times in the light emission intensity ratio atthe peak wavelength of the light emission spectrum, compared to theinorganic fluorescent material La₂O₂S:Eu (KX-681 manufactured by KaseiOptonix, Ltd.). Further, a light emission excitation spectrum wasmeasured. As a result, the excitation wavelength was shifted to the longwavelength side, compared to the inorganic fluorescent materialLa₂O₂S:Eu.

Example 9 Synthesis of Eu(p-DBTBA)₃Phen

In 60 ml of a mixed solvent of tetrahydro-furan/acetonitrile=1/4 (volumeratio), 0.33 g (1.0 mmol) of p-DBTBA represented by the structure shownbelow, 0.07 g (0.33 mmol) of 1,10-phenanthroline monohydrate and 0.11 g(1.0 mmol) of 2,2′-iminodiethanol were dissolved under reflux. To thissolution, a solution obtained by dissolving 0.12 g (0.33 mmol) ofeuropium chloride (III) hexahydrate in 15 ml of a mixed solvent ofethanol/tetrahydrofuran=1/2 (volume ratio) was added dropwise underreflux taking 1 hour. Then, the resulting solution was retained at 60°C., 40° C., 25° C. and 0° C., respectively, for every 1 hour. Aprecipitate thus formed was filtered by suction, and washed withethanol. The resulting light yellow powder was dried under vacuum at100° C. to obtain Eu(p-DBTBA)₃Phen.

The light emission spectrum at excitation of 405 nm of thisEu(p-DBTBA)₃Phen was confirmed. As a result, there was obtained a lightemission intensity of 3.2 times in the area ratio of the light emissionspectrum, and that of 2.4 times in the light emission intensity ratio atthe peak wavelength of the light emission spectrum, compared to theinorganic fluorescent material La₂O₂S:Eu (KX-681 manufactured by KaseiOptonix, Ltd.). Further, a light emission excitation spectrum wasmeasured. As a result, the excitation wavelength was shifted to the longwavelength side, compared to the inorganic fluorescent materialLa₂O₂S:Eu.

Example 10 Synthesis of Eu(o-DBTBA)₃(TPPO)₂

In 40 ml of ethanol, 0.33 g (1.0 mmol) of o-DBTBA represented by thestructure shown below, 0.19 g (0.67 mmol) of triphenylphosphine oxide(hereinafter referred to as TPPO) and 0.11 g (1.0 mmol) of2,2′-iminodiethanol were dissolved. To this solution, a solutionobtained by dissolving 0.12 g (0.33 mmol) of europium chloride (III)hexahydrate in 10 ml of ethanol was added dropwise under reflux taking 1hour. Then, after retention at 40° C. for 2 hours, the resultingsolution was allowed to stand at room temperature for about 15 hours. Aprecipitate thus formed was filtered by suction, and washed withethanol. The resulting light yellow powder was dried under vacuum at100° C. to obtain Eu(o-DBTBA)₃(TPPO)₂.

This Eu(o-DBTBA)₃(TPPO)₂ was irradiated with LED light having a peakwavelength of 400 nm. As a result, red light emission was confirmed.

Example 11 Synthesis of Eu(AQ1SA)₃Phen

In 80 ml of a mixed solvent of ethanol/water=1/2 (volume ratio), 0.93 g(3.0 mmol) of sodium anthraquinone-1-sulfonate, and 0.20 g (1.0 mmol) ofPhen were dissolved under heating (about 60° C.). To this solution, asolution obtained by dissolving 0.37 g (1 mmol) of europium chloride(III) hexahydrate in 20 ml of ethanol was added dropwise at 60° C.taking 1 hour. After reflux for 1 hour, the resulting solution wasallowed to cool to room temperature. A precipitate thus formed wasfiltered by suction, and washed with water. The resulting yellow powderwas dried under vacuum at 100° C., and heat treated at 160° C. for 1hour to obtain Eu(AQ1SA)₃Phen. AQ1SA represents anthraquinone-1-sulfonicacid.

This Eu(AQ1SA)₃Phen was irradiated with LED light having a peakwavelength of 400 nm. As a result, red light emission was confirmed.

Example 12 Synthesis of Eu(o-DBTBSA)₃Phen

In 80 ml of a mixed solvent of tetrahydro-furan/ethanol=9/1 (volumeratio), 0.51 g (1.5 mmol) of o-DBTBSA represented by the structure shownbelow, 0.10 g (0.5 mmol) of 1,10-phenanthroline monohydrate and 0.16 g(1.5 mmol) of 2,2′-iminodiethanol were dissolved under reflux. To thissolution, a solution obtained by dissolving 0.17 g (0.50 mmol) ofeuropium chloride (III) hexahydrate in 15 ml of a mixed solvent ofethanol/tetrahydrofuran=3/1 (volume ratio) was added dropwise underreflux taking 1 hour. Then, the resulting solution was allowed to coolto room temperature. To this solution, 80 ml of ethanol was slowlyadded, and a precipitate formed was filtered by suction and washed withethanol. The resulting yellowish brown powder was dried under vacuum at100° C., and then, heat treated at 160° C. for 1 hour to obtainEu(o-DBTBSA)₃Phen.

This Eu(o-DBTBSA)₃Phen was irradiated with LED light having a peakwavelength of 400 nm. As a result, red light emission was confirmed.

Example 13 Synthesis of Eu(IQSA)₃Phen

In 50 ml of ethanol, 0.63 g (3.0 mmol) of isoquinoline-5-sulfonic acid(hereinafter referred to as IQSA), 0.20 g (1.0 mmol) of1,10-phenanthroline monohydrate and 0.32 g (3.0 mmol) of2,2′-iminodiethanol were dissolved under reflux. To this solution, asolution obtained by dissolving 0.37 g (1.0 mmol) of europium chloride(III) hexahydrate in 20 ml of ethanol was added dropwise under refluxtaking 1 hour. After further reflux for 1 hour, the resulting solutionwas allowed to cool to room temperature. A precipitate formed wasfiltered by suction and washed with ethanol. The resulting white powderwas dried under vacuum at 100° C., and then, heat treated at 160° C. for1 hour to obtain Eu(IQSA)₃Phen.

This Eu(IQSA)₃Phen was irradiated with LED light having a peakwavelength of 375 nm. As a result, red light emission was confirmed.

Example 14 Synthesis of Eu(DPPA)₃Phen

Eu(DPPA)₃Phen was obtained in the same manner as in Example 13 with theexception that IQSA was replaced by 3.0 mmol of diphenylphosphinic acid(DPPA) represented by the structure shown below.

This Eu(DPPA)₃Phen was irradiated with LED light having a peakwavelength of 400 nm. As a result, red light emission was confirmed.

Example 15 Synthesis of Tb(o-DBFBA)₃Phen

In 50 ml of ethanol, 0.95 g (3.0 mmol) of o-DBFBA represented by thestructure below, 0.20 g (1.0 mmol) of 1,10-phenanthroline monohydrateand 0.32 g (3.0 mmol) of 2,2′-iminodiethanol were dissolved underreflux. To this solution, a solution obtained by dissolving 0.37 g (1.0mmol) of terbium chloride (III) hexahydrate in 20 ml of ethanol wasadded dropwise under reflux taking 1 hour. Then, the resulting solutionwas allowed to cool to room temperature, and allowed to stand at roomtemperature for about 15 hours. A precipitate thus formed was filteredby suction, and washed with ethanol. The resulting white powder wasdried under vacuum at 80° C., and then, heat treated at 160° C. for 1hour to obtain Tb(o-DBFBA)₃Phen.

This Tb(o-DBFBA)₃Phen was irradiated with LED light having a peakwavelength of 375 nm. As a result, green light emission was confirmed.

Example 16 Synthesis of Tb(o-DBTBA)₃Phen

In 50 ml of ethanol, 0.99 g (3.0 mmol) of o-DBTBA represented by thestructure shown below, 0.20 g (1.0 mmol) of 1,10-phenanthrolinemonohydrate and 0.32 g (3.0 mmol) of 2,2′-iminodiethanol were dissolvedunder reflux. To this solution, a solution obtained by dissolving 0.37 g(1.0 mmol) of terbium chloride (III) hexahydrate in 20 ml of ethanol wasadded dropwise under reflux taking 1 hour, and the resulting solutionwas allowed to cool to room temperature. A precipitate thus formed wasfiltered by suction, and washed with ethanol. The resulting white powderwas recrystallized from a THF solution, and dried under vacuum at 80° C.to obtain Tb(o-DBTBA)₃Phen.

This Tb(o-DBTBA)₃Phen was irradiated with LED light having a peakwavelength of 375 nm. As a result, green light emission was confirmed.

While the present invention has been described in detail with referenceto specific embodiments thereof, it will be apparent to one skilled inthe art that various changes and modifications can be made thereinwithout departing from the spirit and scope thereof.

This application is based on Japanese Patent Application No. 2003-144388filed on May 22, 2003, the entire content thereof being hereinincorporated by reference.

INDUSTRIAL APPLICABILITY

According to the present invention, there can be provided a lightemitting device which can generate high-intensity light emission, usinga fluorescent material containing a rare earth element ion complex andbeing excellent in durability, and the fluorescent material to be usedtherein.

1. A light emitting device comprising a semiconductor light emittingelement which emits light within the region from near-ultraviolet lightto visible light, and a fluorescent material which contains a rare earthelement ion complex having an aromatic ring-containing Bronsted acid ionwith a pKa value of 7 or less as a ligand and emits light by the actionof light of said semiconductor light emitting element, wherein aBronsted acid ion represented by general formula (2) shown below, whichis derived from an aromatic ring-containing Bronsted acid represented bygeneral formula (1) shown below, is used as said ligand

wherein R₁ is a group containing at least one aromatic hydrocarbon ringor aromatic heterocycle, each optionally having a substituent group atless than all available positions, X is a divalent connecting group, Qrepresents a carbon, sulfur or phosphorous atom, a represents 1 or 2, nrepresents 0 or 1, and p represents 0 or 1, and wherein when saidBronsted acid is an optionally substituted benzophenone carboxylic acid,the carboxylic acid group lies at an ortho position relative to thecarbonyl group.
 2. The light emitting device according to claim 1,wherein a rare earth element used in a rare earth element ion whichforms said rare earth element ion complex is an element selected fromthe group consisting of praseodymium, samarium, europium, terbium,dysprosium, holmium, erbium and thulium.
 3. The light emitting deviceaccording to claim 2, wherein the rare earth element used in the rareearth element ion which forms the rare earth element ion complex iseuropium or terbium.
 4. The light emitting device according to claim 1,wherein said ligand is one in which the triplet energy of a mothercompound of said Bronsted acid ion is higher than an excited-stateenergy level that is involved in light emission of the rare earthelement ion.
 5. The light emitting device according to claim 1, whereinsaid fluorescent material is a fluorescent material containing a rareearth element ion complex represented by the following general formula(5):A₃LD_(r)  (5) wherein A represents the Bronsted acid ion of said generalformula (2) which may be different from one another, L represents a rareearth element ion, D represents an auxiliary ligand comprising a Lewisbase, and r represents 0, 1 or
 2. 6. The light emitting device accordingto claim 1, wherein said fluorescent material contains a rare earthelement ion complex in which said Bronsted acid ion as a ligand is anaromatic ketone-containing group.
 7. The light emitting device accordingto claim 1, wherein said fluorescent material contains a rare earthelement ion complex having as a ligand said Bronsted acid ion having agroup containing a tricyclic aromatic hydrocarbon and/or a tricyclicaromatic heterocycle.
 8. The light emitting device according to claim 1,wherein said fluorescent material is a resin composition in which saidrare earth element ion complex is mixed or dispersed.
 9. The lightemitting device according to claim 1, wherein said Bronsted acid ion isa carboxylic acid ion or a sulfonic acid ion.
 10. The light emittingdevice according to claim 1, wherein said semiconductor light emittingelement is a laser diode or light emitting diode having a peakwavelength within the range of 360 nm to 470 nm.
 11. The light emittingdevice according to claim 1, wherein the device comprises anotherfluorescent material which emits light by the action of light of saidsemiconductor light emitting element, together with the fluorescentmaterial containing rare earth element ion complex, which emits light bythe action of light of said semiconductor light emitting element. 12.The light emitting device according to claim 1, wherein the lightemitting device is a lighting system.